In cataract surgery, the natural lens is removed. To refocus the light on the retina and thus restore vision, an intraocular lens is implanted in place of the natural lens.
The intraocular lens can be implanted at various locations within the eye, such as within the capsular bag in the posterior chamber. After implantation of the intraocular lens in the capsular bag, it is sometimes necessary to perform a surgical technique known as discission in which an opening is formed in the posterior capsule. Discission has been performed with mechanical cutting instruments, such as a needle, and more recently, with a surgical laser. Discission may be necessary, for example, to restore vision that has become clouded following implantation of the intraocular lens.
A typical intraocular lens includes an optic and fixation members, with the optic having a flat posterior surface which seats against the posterior capsule. To avoid pitting of the posterior surface of the optic when discission is carried out with a surgical laser, it is necessary to space the posterior surface from the posterior capsule.
One way of spacing the posterior surface of the optic from the posterior capsule is to form an annulus on the posterior surface of the optic, and examples of such construction are shown in Shearing U.S. Pat. No. 4,159,546 and Hoffer U.S. Pat. No. 4,244,060. Alternatively, the posterior surface of the optic can be made concave so that the posterior periphery of the optic engages the posterior capsule with central regions of the posterior surface being spaced from the posterior capsule. Unfortunately, these annular posterior projections on the optic tend to hamper insertion of the intraocular lens into the eye. More specifically, the annular projection is difficult to slide across the iris and causes portions of the iris, in effect, to build up in front of the advancing projection.
The annular projections have other disadvantages. For example, they add weight to the intraocular lens and tend to inhibit the escape of tissue debris or cortical remnants. If the optic becomes decentered, the annular projection may cause visual aberrations. The annular projection may also enable wrinkles to form in the posterior capsule. Wrinkles are undesirable when discission is being carried out. Finally, gripping of the optic with forceps necessarily involves gripping of the annular projection, and this can cause structural failure of the projection.